Extractive distillation of hexafluoropropylene epoxide mixture



United States Patent 3,326,780 EXTRACTIVE DlSTiLLATION 0F HEXAFLUORO- .PROPYLENE EPOXIDE MIXTURE Herbert Albert Wiist, Vienna, W. Va., assignor to E. I. du

Pont de Nemours and Company, Wilmington, Del., a

corporation of Delaware No Drawing. Filed Dec. 29, 1964, Ser. No. 422,025

7 Claims. (Cl. 203-60) This invention relates to the purification of hexafiuoropropylene epoxide, and, more particularly, to the separation of the epoxide from hexafiuoropropylene by extractive distillation.

Hexafiuoropropylene epoxide is produced by the autoxidation of hexafiuoropropylene. The crude product of the oxidation contains hexafiuoropropylene together with several by-products. Some of the by-products may be removed without difficulty by common techniques of scrubbing and distillation; however, hexafiuoropropylene boils too closely to hexafiuoropropylene epoxide ('29.4 C. and 27.4 C., respectively) to permit separation by conventional distillation. Chemical reaction may be employed to separate the components with the attendant or accompanying loss of hexafiuoropropylene or the necessity for costly processing to recover the reacted material.

The present invention is realized by employing an extractive distillation to separate the above-mentioned epoxide from hexafiuoropropylene after the crude product from the autoxidation has been distilled to remove materials which differ substantially in boiling point from the above-mentioned fluorocarbons. The efficiency of the extractive distillation relies upon the selective effect of a third component which depresses the volatility of hexafiuoropropylene and increases the relative volatility of the fluorocarbons so that they may be separated by distillation. The third component or solvent must not react chemically with the fluorocarbons so that it may be separated from the fluorocarbons by conventional distillation.

Solvents which are operable in the present process include mono-, diand trisubstituted benzenes wherein the substituents are alkyl groups of 1-4 carbon atoms and alkoxy groups of 1-4 carbon atoms, dialkyl ethers of ethylene glycol and diethylene glycol wherein the alkyl groups of the ethers have 1-2 carbon atoms, dialkyl carbonates wherein the alkyl groups have l-4 carbon atoms, carbon tetrachloride and chloroform. The solvent may be present in a weight ratio to the fluorocarbons of from about 1:1 to about 1000A, and preferably from about 10:1 to 80:1. Examples of solvents which have beenvfound to be operable in the present invention and which fall within the above-described class are toluene, the diethyl ether of ethylene glycol, and the diethyl ether of diethylene glycol, carbon tetrachloride, p-Xylene, mxylene, o-xylene, and isomeric mixtures thereof, anisole, p-cymene, butyl phenyl ether, and mesitylene. The preferred solvents are toluene, xylene, anisole, p-cymene, and mesitylene. Other solvents which are within the purview of the present invention include but are not limited to dimethyl carbonate, dibutyl carbonate, n-butyl benzene, isobutyl benzene, tertiary butyl benzene, di-normal-butyl benzene and rnethylethyl benzene, diethyl benzene, triethyl benzene, tributyl benzene, butoxy benzene, propoxy benzene, tributoxy benzene, propoxymethoxy benzene, butoxymethyl benzene, and butoxydimethyl benzene.

The optimum operating conditions will depend upon the desired purity of the epoxide and the effective number of fractionation stages in a given column. Generally, for best results, it is preferable to operate with the temperature of the solvent feed between 5 to 40 C. above the boiling point of the epoxide at the pressure of the distillation. The upper distillation temperature is dictated by Patented June 20, 1967 relative volatility of the fluorocarbons in the presence of the solvent; i.e., the distillation becomes impractical as the relative volatility approaches 1.

The following examples are presented to illustrate and not to restrict the present invention. Parts and percentages are by weight unless otherwise noted.

Example 1 A batch distillation was conducted using a laboratory column (one inch diameter, 36 inches in height) packed with Podbielniak Heli-pak packing which by calibration with known mixtures was determined to have about 23 theoretical stages. Approximately grams of a mixture containing 45 percent hexafiuoropropylene and 55 percent hexafiuoropropylene epoxide was charged to the pot and dimethoxyethane precooled to between 22 to --30 C., was continuously introduced into the top of the column at a rate of approximately 25 cc. per minute. Boilup was established by applying heat to the pot and the condensate was routed to provide total reflux. After equilibrium had been approached as evidenced by overhead temperature of approximately -29 C., a base temperature of -23 C. and a pot temperature of approximately +24 C., samples were taken of the overhead vapor and of the pot vapor. Analysis showed the overhead vapor to contain 99.5 mol percent hexafiuoropropylene epoxide and the pot vapor to contain 3-8.8 mol percent of the epoxide. Calculations based on the Fenske equation indicated a relative volatility of approximately 1.30.

Example 2 Using the same equipment and procedure of Example 1, toluene cooled to approximately --40 C. was introduced at a rate of about 25 cc. per minute in place of the dimethoxy ethane of Example 1. After the system had reached equilibrium at total reflux, the overhead vapor contained 99.4 mol percent of the epoxide and the pot vapor contained 17.0 mol percent of the epoxide.

The foregoing examples illustrate the effectiveness of the separation of the present invention which is impractical with normal distillation techniques. Solvents such as ethyl acetate, dioxane, benzene, n-decane, ethanol and ethyl acetophenone which are outside of the class disclosed hereinabove but which are closely related to the above-described solvents do not depress the volatility of the hexafiuoropropylene to permit separation by distillation.

As illustrated from the foregoing specification, the process of the present invention provides an economical route for the recovery of hexafiuoropropylene epoxide, a valuable chemical and intermediate material.

I claim:

1. A process for the separation of hexafiuoropropylene from hexafiuoropropylene epoxide by extractive distilla tion in the presence of a normally liquid compound selected from the class consisting of mono-, diand trisubstituted benzene wherein the substituents are selected from the class consisting of alkyl groups having 14 carbon atoms and alkoxy groups having 1-4 carbon atoms, dialkyl ethers of ethylene glycol and diethylene glycol wherein the alkyl groups of the ethers have 1-2 carbon atoms, dialkyl carbonates wherein the alkyl groups have 1-4 carbon atoms, carbon tetrachloride and chloroform.

2. A process for the recovery of hexafiuoropropylene epoxide from a mixture of said epoxide with hexafluoropropylene which comprises distilling said mixture in the presence of a normally liquid compound selected from the class consisting of mono-, diand trisubstituted benzenes wherein the substituents are selected from the class consisting of alkyl groups having 1-4 carbon atoms and alkoxy groups having 1-4 carbon atoms, dialkyl ethers of ethylene glycol and diethylene glycol wherein the alkyl group has 1-2 carbon atoms, dialkyl carbonates wherein the alkyl groups have 1-4 carbon atoms, carbon tetrachloride and chloroform to produce a vapor composed substantially of said epoxide' and thereafter condensing said vapor.

3.The process of claim 1 wherein the normally liquid compound is toluene.

4. The process of claim compound is xylene.

5. The process of claim 1 wherein said normally liquid compound is anisole.

6. The process of claim 1 wherein said normally liquid compound is p-cymene.

7. The process of claim 1 wherein said normally liquid compound is mesitylene.

1 wherein said normally liquid 4 References Cited UNITED STATES PATENTS 7/1943 Durrum 203-58 X 4/1955 Morrell et a1. 203-57 X 8/1963 Wiist 203-67 3/1964 Warnell 260-3485 X 11/1966 Wiist 203-63 X FOREIGN PATENTS 10/1961 France.

4/1962 Belgium.

NORMAN YUDKOFF, Primary Examiner.

15 F. E. DRUMMOND, Assistant Examiner. 

1. A PROCESS FOR THE SEPARATION OF HEXAFLUOROPROPYLENE FROM HEXAFLUOROPROPYLENE EPOXIDE BY EXRACTIVE DISTILLATION IN THE PRESENCE OF A NORMALLY LIQUID COMPOUND SELECTED FROM THE CLASS CONSISTING OF MONO-, DI- AND TRISUBSTITUTED BENZENE WHEREIN THE SUBSTITUENTS ARE SELECTED FROM THE GLASS CONSISTING OF ALKYL GROUP HAVING 1-4 ATOMS, DIALKYL ETHERS OF ETHYLENE GLYCOL AND DIETHYLENE GLYCOL WHEREIN THE ALKYL GROUPS OF THE ETHERS HAVE 1-2 CARBON ATOMS, DIALKYL CARBONATES WHEREIN THE ALKYL GROUPS HAVE 1-4 CARBON ATOMS, CARBON TETRACHLORIDE AND CHLOROFORM. 